Combined whole-body vibration, resistance exercise, and sustained vascular occlusion increases PGC-1α and VEGF mRNA abundances

We previously reported that high load resistance exercise with superimposed whole-body vibration and sustained vascular occlusion (vibroX) markedly improves cycling endurance capacity, increases capillary-to-fibre ratio and skeletal muscle oxidative enzyme activity in untrained young women. These findings are intriguing, since increases in oxidative muscle phenotype and endurance capacity are typically induced by endurance but not heavy resistance exercise. Here, we tested the hypothesis that vibroX activates genes associated with mitochondrial biogenesis and angiogenesis. Eight healthy, recreationally resistance-trained young men performed either vibroX or resistance exercise (RES) in a randomised, cross-over design. Needle biopsies (M. vastus lateralis) were obtained at rest and 3h post-exercise. Changes in relative gene expression levels were assessed by real-time quantitative PCR. After vibroX, vascular endothelial growth factor and peroxisome proliferator-activated receptor-γ coactivator 1α mRNA abundances increased to 2- and 4.4-fold, respectively, but did not significantly change above resting values after RES. Other genes involved in mitochondrial biogenesis were not affected by either exercise modality. While vibroX increased the expression of hexokinase II, xanthine dehydrogenase, and manganese superoxide dismutase mRNA, there were no changes in these transcripts after RES. This study demonstrates that high load resistance exercise with superimposed whole-body vibration and sustained vascular occlusion activates metabolic and angiogenic gene programs, which are usually activated after endurance but not resistance exercise. Thus, targeted modification of high load resistance exercise by vibration and vascular occlusion might represent a novel strategy to induce endurance-type muscle adaptation

Short-term HFD does not alter lipolytic function of adipocytes

A short bout of high fat diet (HFD) impairs glucose tolerance and hepatic insulin sensitivity. We recently identified adipose tissue inflammation and resulting dysfunctional adipose tissue-liver cross-talk as an early event in the development of HFD-induced hepatic insulin resistance. In particular, reducing white adipose tissue (WAT) inflammation by adipocyte-specific depletion of Fas/CD95 protected mice from developing hepatic insulin resistance but not hepatic steatosis. Herein, we expanded our previous work and determined the impact of four days of HFD on lipolytic activity of isolated adipocytes. Compared with chow-fed mice, the degree of basal and isoproterenol-stimulated free fatty acid (FFA) and glycerol release was similar in HFD-fed animals. Moreover, insulin's ability to suppress lipolysis remained intact, suggesting retained insulin sensitivity. Despite unaltered lipolysis, circulating FFA concentrations were greatly increased in non-fasted HFD-fed mice. In conclusion, a short-term HFD challenge does not affect lipolytic function of adipocytes. The observed increase of circulating FFA levels in randomly fed animals may rather be the result of increased dietary fat supply

ASK1 inhibits browning of white adipose tissue in obesity

Increasing energy expenditure via induction of adipose tissue browning has become an appealing strategy to treat obesity and associated metabolic complications. Herein, we identify adipocyte-expressed apoptosis signal-regulating kinase 1 (ASK1) as regulator of adipose tissue browning. High fat diet-fed adipocyte-specific ASK1 knockout mice reveal increased UCP1 protein levels in inguinal adipose tissue concomitant with elevated energy expenditure, reduced obesity and ameliorated glucose tolerance compared to control littermates. In addition, ASK1-depletion blunts LPS-mediated downregulation of isoproterenol-induced UCP1 in subcutaneous fat both in vitro and in vivo. Conversely, adipocyte-specific ASK1 overexpression in chow-fed mice attenuates cold-induced UCP1 protein levels in inguinal fat. Mechanistically, ASK1 phosphorylates interferon regulatory factor 3 (IRF3) resulting in reduced Ucp1 expression. Taken together, our studies unravel a role of ASK1 in mediating the inhibitory effect of caloric surplus or LPS-treatment on adipose tissue browning. Adipocyte ASK1 might be a pharmacological target to combat obesity and associated morbidities

Combined whole-body vibration, resistance exercise, and sustained vascular occlusion increases PGC-1α and VEGF mRNA abundances

We previously reported that high load resistance exercise with superimposed whole-body vibration and sustained vascular occlusion (vibroX) markedly improves cycling endurance capacity, increases capillary-to-fibre ratio and skeletal muscle oxidative enzyme activity in untrained young women. These findings are intriguing, since increases in oxidative muscle phenotype and endurance capacity are typically induced by endurance but not heavy resistance exercise. Here, we tested the hypothesis that vibroX activates genes associated with mitochondrial biogenesis and angiogenesis. Eight healthy, recreationally resistance-trained young men performed either vibroX or resistance exercise (RES) in a randomised, cross-over design. Needle biopsies (M. vastus lateralis) were obtained at rest and 3 h post-exercise. Changes in relative gene expression levels were assessed by real-time quantitative PCR. After vibroX, vascular endothelial growth factor and peroxisome proliferator-activated receptor-γ coactivator 1α mRNA abundances increased to 2- and 4.4-fold, respectively, but did not significantly change above resting values after RES. Other genes involved in mitochondrial biogenesis were not affected by either exercise modality. While vibroX increased the expression of hexokinase II, xanthine dehydrogenase, and manganese superoxide dismutase mRNA, there were no changes in these transcripts after RES. This study demonstrates that high load resistance exercise with superimposed whole-body vibration and sustained vascular occlusion activates metabolic and angiogenic gene programs, which are usually activated after endurance but not resistance exercise. Thus, targeted modification of high load resistance exercise by vibration and vascular occlusion might represent a novel strategy to induce endurance-type muscle adaptations

Opposing effects of reduced kidney mass on liver and skeletal muscle insulin sensitivity in obese mice

Reduced kidney mass and/or function may result in multiple metabolic derangements, including insulin resistance. However, underlying mechanisms are poorly understood. Herein, we aimed to determine the impact of reduced kidney mass on glucose metabolism in lean and obese mice. To that end, seven-week-old C57BL6/J mice underwent uninephrectomy (UniNx) or sham operation. After surgery, animals were fed either a chow (standard) or a high fat diet (HFD) and glucose homeostasis was assessed 20 weeks after surgery. Intraperitoneal glucose tolerance was similar in sham-operated and UniNx mice. However, insulin-stimulated glucose disposal in vivo was significantly diminished in UniNx mice, whereas insulin-stimulated glucose uptake into isolated skeletal muscle was similar in sham-operated and UniNx mice. Of note, capillary density was significantly reduced in skeletal muscle of HFD-fed UniNx mice. In contrast, hepatic insulin sensitivity was improved in UniNx mice. Furthermore, adipose tissue HIF1α-expression and inflammation was reduced in HFD-fed UniNx mice. Treatment with the angiotensin II receptor blocker telmisartan improved glucose tolerance and hepatic insulin sensitivity in HFD-fed sham-operated but not UniNx mice. In conclusion, UniNx protects from obesity-induced adipose tissue inflammation and hepatic insulin resistance but it reduces muscle capillary density and, thus, deteriorates HFD-induced skeletal muscle glucose disposal

Aerobic function and skeletal muscle plasticity in health and disease

In recent decades, chronic diseases have reached epidemic proportions in the industrialised world. A physically inactive lifestyle has been identified as a major factor causing maladaptations leading to coronary heart disease, stroke, hypertension, type 2 diabetes, osteoporosis, breast cancer, and colon cancer. Regular physical activity prevents the development of obesity and induces a multitude of favourable adaptations within skeletal muscle and the cardio-respiratory system, which have positive outcomes for both the prevention and treatment of metabolic diseases. Specifically, high aerobic function is related to physical activity whereas low aerobic function is related to physical inactivity and various metabolic diseases. In order to gain a better understanding of the mechanisms underlying aerobic function and skeletal muscle plasticity it is fundamental to identify which specific exercise stimuli leads to what molecular response, and how this molecular response relates to the structural, contractile, and metabolic adaptation. Thus, the present thesis was aimed at providing new insights into the mechanisms underlying aerobic function and skeletal muscle plasticity by using an integrative approach including cell culture, rodent, and human models. In a first study, in order to shed light upon the relationship of aerobic function and type 1 diabetes, we investigated factors that may limit oxidative capacity and aerobic exercise performance in young untrained women with type 1 diabetes. Calf muscle oxidative capacity was not different between untrained women with type 1 diabetes and healthy women of similar age and activity levels. Notably, HbA1c was negatively correlated with mitochondrial capacity in women with type 1 diabetes. Although HbA1c was negatively correlated with cardiac output in women with type 1 diabetes, maximal oxygen consumption, cardiac output, endurance capacity, skeletal muscle oxidative enzyme activity, and capillary-to-fibre ratio were not reduced in women with type 1 diabetes compared to healthy women. These results indicate that oxidative capacity depends on HbA1c in untrained women with type 1 diabetes but aerobic function is not reduced relative to untrained healthy women. Thus, it is important to accurately control glycaemic status in future studies investigating the aerobic function in patients with type 1 diabetes. In a second study, we aimed at establishing a cell culture model to closely recapitulate the plastic changes in gene expression as observed in aerobically trained skeletal muscles of mice. In electrically stimulated C2C12 mouse muscle cells the transcriptional adaptations were almost identical to those in endurance-trained skeletal muscles of mice, but differed from the acute effects of exercise on muscle gene expression. In addition, significant alterations in the expression of myofibrillar proteins indicated that this in vitro exercise model could be used to modulate the fibre-type of muscle cells in culture. Our data thus describe an experimental cell culture model for the study of at least some of the transcriptional aspects of skeletal muscle adaptation to physical activity. Typically, aerobic function can be improved by repeated endurance exercise but not by resistance exercise. To overcome the specificity of this adaptive response we aimed in a third study at designing a new resistance exercise model with superimposed stimuli to induce endurance type adaptations and to test its effectiveness in humans. Indeed, 5 weeks of whole-body vibration training with superimposed heavy resistance exercise and sustained vascular occlusion (VRO) increased capillary-to-fibre ratio, skeletal muscle oxidative enzyme activity, myosin heavy chain type 1 fibre proportion, and endurance capacity. In a fourth study, we analysed the molecular bases underlying these adaptations. A single bout of VRO increased the expression of vascular endothelial growth factor (VEGF) mRNA through reactive oxygen species (ROS)-activated peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) probably in a hypoxia-inducible factor 1α (HIF-1α) independent manner. In conclusion, modified high-intensity resistance exercise activates gene programmes typically linked to endurance exercise. In den letzten Jahrzehnten haben chronische Krankheiten in der industrialisierten Welt epidemieartig zugenommen. Ein körperlich inaktiver Lebensstil gilt als Hauptursache für viele verschiedene Krankheiten wie koronare Herzkrankheit, Schlaganfall, Bluthochdruck, Typ 2 Diabetes, Osteoporose, Brust- und Darmkrebs. Regelmässige körperliche Aktivität kann die Entstehung von Fettleibigkeit verhindern und zu vielen Anpassungen in der Skelettmuskulatur und im Herzkreislaufsystem führen und dadurch Stoffwechselerkrankungen entgegenwirken. Insbesondere hängt eine gute aerobe Muskelfunktion mit körperlicher Aktivität zusammen, währenddem eine verminderte aerobe Muskelfunktion mit körperlicher Inaktivität und vielen Stoffwechselerkrankungen in Zusammenhang gebracht wird. Um ein besseres Verständnis der Mechanismen der aeroben Muskelfunktion und -plastizität zu erhalten, ist es notwendig zu verstehen, welche spezifischen Trainingsreize zu welcher molekularen Antwort führen und welche molekularen Antworten welche strukturellen, kontraktilen und metabolischen Adaptationen verursachen. Aus diesem Grund bestand das Ziel der vorliegenden Arbeit darin, neue Erkenntnisse über die aerobe Muskelfunktion und -plastizität zu erlangen. Zu diesem Zweck haben wir in unseren Studien einen integrativen Ansatz gewählt und dabei Zellkultur-, Nagetier- und Humanmodelle angewendet. In der ersten Studie untersuchten wir den Zusammenhang zwischen aerober Muskelfunktion und Typ 1 Diabetes. Wir haben Faktoren, welche die oxidative Kapazität und aerobe Leistungsfähigkeit determinieren, in untrainierten jungen Frauen mit Typ 1 Diabetes gemessen und mit gesunden untrainierten Frauen im gleichen Alter verglichen. Die oxidative Kapazität im Unterschenkelmuskel hat sich zwischen untrainierten jungen Frauen mit Typ 1 Diabetes und gesunden untrainierten Frauen im gleichen Alter nicht unterschieden. Bemerkenswert ist, dass bei den Typ 1 Diabetikerinnen das HbA1c negativ mit der mitochondrialen Kapazität korrelierte. Obwohl bei den Typ 1 Diabetikerinnen das HbA1c auch mit dem Herzminutenvolumen negativ korrelierte, waren die maximale Sauerstoffaufnahme, Herzminutenvolumen, Aus- dauerleistungsfähigkeit, Aktivität von oxidativen Enzymen in der Skelettmuskulatur und das Verhältnis der Kapillaren zu den Skelettmuskelfasern, im Vergleich mit gleichaltrigen gesunden Frauen, nicht vermindert. Diese Ergebnisse zeigen auf, dass bei untrainierten Frauen mit Typ 1 Diabetes die oxidative Kapazität vom HbA1c abhängig ist, die aerobe Muskelfunktion verglichen mit gesunden untrainierten Frauen aber nicht vermindert ist. Daher ist es wichtig, in zukünftigen Studien das HbA1c sorgfältig zu kontrollieren, wenn man die aerobe Muskelfunktion untersuchen will. In einer zweiten Studie entwickelten wir ein Zellkulturmodell, in welchem wir die gleichen Genexpressionsveränderungen beobachten konnten, wie in Skelettmuskeln von ausdauertrainierten Mäusen. In elektrisch stimulierten C2C12 Mausmuskelzellen waren die transkriptionellen Adaptationen beinahe identisch mit denen in Skelettmuskeln von ausdauertrainierten Mäusen. Sie unterschieden sich aber von den akuten transkriptionellen Antworten in Skelettmuskeln von Mäusen. Zudem zeigten sich signifikante Veränderungen in der Expression von myofibrillären Proteinen. Unsere Studienergebnisse zeigen, dass wir dieses Zellkulturmodell dafür verwenden können, um transkriptionelle Veränderungen im Skelettmuskel nach körperlicher Aktivität und Veränderungen des Skelettmuskelfasertypus zu untersuchen. Üblicherweise kann die aerobe Muskelfunktion mit regelmässigem Ausdauertraining nicht aber mit Krafttraining verbessert werden. Um diese spezifischen Anpassungen zu umgehen, haben wir in einer dritten Studie ein neuartiges Trainingsmodell entwickelt. Unser Ziel war es, mit einem modifizierten Krafttraining Adaptionen hervorzurufen, welche normalerweise mit Ausdauertraining einhergehen. Das modifizierte Krafttraining bestand aus einer Kombination aus intensivem Vibrations- und Krafttraining mit gleichzeitig unterbundenem Blutfluss zu und aus den Beinen. Wir konnten zeigen, dass fünf Wochen modifiziertes Krafttraining zu einem erhöhten Verhältnis der Kapillaren zu den Skelettmuskelfasern führte und dies mit einer erhöhten Aktivität von oxidativen Enzymen in den Skelettmuskeln einherging. Zudem nahm der Anteil der Typ I Muskelfasern und die Ausdauerleistungsfähigkeit zu. In der vierten Studie untersuchten wir die molekularen Mechanismen, welche zu den beschriebenen Adaptationen führten. Ein einzelnes modifiziertes Krafttraining erhöhte die mRNA Expression von “vascular endothelial growth factor” (VEGF) und “peroxisome proliferator-activated receptor γ coactivator 1α” (PGC-1α). Möglicherweise aktivierten “reactive oxygen species” (ROS) flussabwärts PGC-1α, welches weiter VEGF auf eine “hypoxia-inducible factor 1α” (HIF-1α) unabhängige Weise induzierte. Unsere Studienergebnisse belegen, dass ein modifiziertes hochintensives Krafttraining Genprogramme induzieren kann, welche üblicherweise nach Ausdauertraining beobachtet werden

Mesenteric Fat Lipolysis Mediates Obesity-associated Hepatic Steatosis and Insulin Resistance

Hepatic steatosis and insulin resistance are among the most prevalent metabolic disorders and tightly associated with obesity and type 2 diabetes. However, underlying mechanism linking obesity to hepatic lipid accumulation and insulin resistance are incompletely understood. Glycoprotein 130 (gp130) is the common signal transducer of all interleukin 6 (IL-6) cytokines. Herein, we provide evidence that gp130-mediated adipose tissue lipolysis promotes hepatic steatosis and insulin resistance. In obese mice, adipocyte-specific gp130 deletion reduced basal lipolysis and enhanced insulin's ability to suppress lipolysis from mesenteric but not epididymal adipocytes. Consistently, free fatty acid levels were reduced in portal but not in systemic circulation of obese knockout mice. Importantly, adipocyte-specific gp130 knockout mice were protected from high fat diet (HFD)-induced hepatic steatosis as well as insulin resistance. In humans, omental but not subcutaneous IL-6 mRNA expression correlated positively with liver lipid accumulation (r=0.31; p<0.05) and negatively with euglycemic clamp glucose infusion rate (r=-0.28; p<0.05). Our results demonstrate that IL-6 cytokine-induced lipolysis may be restricted to mesenteric WAT and that it contributes to hepatic insulin resistance and steatosis. Therefore, blocking IL-6 cytokine signaling in (mesenteric) adipocytes may be a novel approach to blunt detrimental fat-liver crosstalk in obesity

Adipose tissue inflammation contributes to short-term high-fat diet-induced hepatic insulin resistance

High-fat feeding for 3-4 days impairs glucose tolerance and hepatic insulin sensitivity. However, it remains unclear whether the evolving hepatic insulin resistance is due to acute lipid overload or the result of induced adipose tissue inflammation and consequent dysfunctional adipose tissue-liver cross-talk. In the present study, feeding C57Bl6/J mice a fat-enriched diet [high-fat diet (HFD)] for 4 days induced glucose intolerance, hepatic insulin resistance (as assessed by hyperinsulinemic euglycemic clamp studies), and hepatic steatosis as well as adipose tissue inflammation (i.e., TNFα expression) compared with standard chow-fed mice. Adipocyte-specific depletion of the antiapoptotic/anti-inflammatory factor Fas (CD95) attenuated adipose tissue inflammation and improved glucose tolerance as well as hepatic insulin sensitivity without altering the level of hepatic steatosis induced by HFD. In summary, our results identify adipose tissue inflammation and resulting dysfunctional adipose tissue-liver cross-talk as an early event in the development of HFD-induced hepatic insulin resistance

ASK1 inhibits browning of white adipose tissue in obesity

ncreasing energy expenditure via induction of adipose tissue browning has become an appealing strategy to treat obesity and associated metabolic complications. Herein, we identify adipocyte-expressed apoptosis signal-regulating kinase 1 (ASK1) as regulator of adipose tissue browning. High fat diet-fed adipocyte-specific ASK1 knockout mice reveal increased UCP1 protein levels in inguinal adipose tissue concomitant with elevated energy expenditure, reduced obesity and ameliorated glucose tolerance compared to control littermates. In addition, ASK1-depletion blunts LPS-mediated downregulation of isoproterenol-induced UCP1 in subcutaneous fat both in vitro and in vivo. Conversely, adipocyte-specific ASK1 overexpression in chow-fed mice attenuates cold-induced UCP1 protein levels in inguinal fat. Mechanistically, ASK1 phosphorylates interferon regulatory factor 3 (IRF3) resulting in reduced Ucp1 expression. Taken together, our studies unravel a role of ASK1 in mediating the inhibitory effect of caloric surplus or LPS-treatment on adipose tissue browning. Adipocyte ASK1 might be a pharmacological target to combat obesity and associated morbidities.ISSN:2041-172